The read/write performance of a computer hard disc drive varies as its temperature varies. This is true both for the electrical and mechanical properties of a hard drive disc which are affected by these temperature changes. For instance, various electrical features such as head-load performance and reliability as well as read signal magnitude and profile can change as a function of these temperature changes. In addition, its seek performance tends to decrease as its temperature increases due to changes in the servo system gains. Various mechanical constraints such as the thickness of the actuator bearing grease are also known to be temperature dependent. At cooler temperatures, the actuator bearing grease becomes thicker and the read/write flex of the actuator becomes somewhat stiffer thus increasing biasing forces on the actuator which tend to restrain both its movement and flexibility. Furthermore, tracking error ascribable to thermal expansion of the magnetic head arm corresponding to temperature elevation also results from thermal expansion and dimensional change to the magnetic head and the discs. Moreover, motor performance which is also affected by temperature, changes with the motor winding resistance increasing and bearing grease thickening as the temperature increases. This in turn affects the motor start performance and reliability. Specifically, resistance in the read and write elements of the magneto-resistive (MR) heads increase and the performance of the electronic components (such as the gain, frequency response, propagation delays and noise) in general degrade at higher temperatures.
These temperature dependent problems are somewhat unavoidable as the disc drive itself will heat up after either a long period of operation or by the raising of ambient temperatures. Most commonly, this temperature elevation occurring in the hard disc is mostly due to thermal energy being emitted by the drive electronics, and to a lesser degree by windage loss due to the disc's rotation.
Since temperature has many adverse effects on hard drive performance and since these effects tend to change in response to temperature changes, equipping a hard disc drive of a computer with a temperature measuring mechanism would allow this hard drive to be designed or operated so as to compensate for these various temperature changes. This would thus ensure maximum drive performance and reliability under various and changing temperature environments. In addition, determining and recording the temperature in the disc drive when an error occurs could provide valuable information which could later be used to assist in determining the cause of the error.
Various prior art systems are directed to temperature-based problems occurring in computer hard disk drives, but these systems are all quite limiting for reasons discussed herein. For example, the problem of temperature changes causing the unwanted movement of a magnetic head attached to an actuator arm in a magnetic disc drive was noted in U.S. Pat. No. 5,440,437 to Sanada, et al. As a way of compensating for movement caused by the thermal expansion and contraction of the actuator arm, this patent discloses a magnetic head arm being partially constituted by a member of a different co-efficient of thermal expansion than the remaining portion of the magnetic head arm. Accordingly, this system was able to correct for tracking errors ascribable to the thermal expansion of the magnetic head arm at varying ambient temperatures. Only being designed to correct for tracking errors caused by the thermal expansion and contraction of the magnetic arm, the Sanada system is not enabled to provide any measuring and feedback of the ambient temperature such that other temperature dependent phenomenon including read signal magnitude and profile, bearing grease thickness, magnetic head arm flexure, seek performance, motor performance and motor winding resistance could be compensated for at varying temperatures.
Various other systems exist for compensating for temperature dependent factors affecting hard drive performance, but these systems all tend to be restricted to preventing, rather than compensating for, these effects. For example, a system for positioning a magnetic head of a magnetic disc device such that the heat produced by the stepping motor has no significant influence on the magnetic head support is disclosed in U.S. Pat. No. 4,796,121 to Adamek, et al. This system does not provide any measuring and feedback of ambient temperatures but rather is directed entirely to shielding the magnetic head from damaging heat using a foil with satisfactory heat sinking properties to shield the motor.
Another system for compensating for temperature-based effects in a magnetic disc memory is provided in U.S. Pat. No. 3,723,980 to Gabor. In this system, the various parts of the disc drive are all kept at substantially uniform temperature by controlled air flow and any thermal expansion/contraction changes are compensated for by the use of similar materials in similar locations in the design of the magnetic disc memory unit. Accordingly, this system only provides temperature compensation with respect to the thermal expansion or contraction of its various mechanical parts. This device is not, however, adapted to measure or provide feedback as to these various temperature changes such that temperature compensation could be provided for various other temperature dependent concerns such as the density of bearing grease or the flexibility of the mechanical actuator arm.
A device exists for laser sensing the temperature of a rotating disc cartridge by forming the disc cartridge out of the same material as the disc itself so as to avoid an orifice being cut in the disc to be used in conjunction with a radiation thermometer. Such a system is disclosed in U.S. Pat. No. 5,182,742 to Ohmori, et al. This system is, however, designed solely to measure the temperature in a disc cartridge and is not adapted to measure or compensate for temperature changes in the magnetic head assembly of a hard disc drive.
A number of systems exist for cooling disc drives. Examples are disclosed in U.S. Pat. No. 4,488,192 to Treseder and U.S. Pat. No. 5,041,931 to Uno, et al. Unfortunately, these systems operate simply to cool the disc drives and are not adapted to measure or provide feedback as to the temperatures or temperature changes occurring in these hard disc drives.
As can be appreciated, none of the above systems satisfy a long-felt need for a system which is adapted to measure the temperature in a computer hard disc drive such that this temperature feedback can be used in both the design and the control operation of various systems for compensating for the effects of temperature variance in the computer disc drive.